mina is smelted by subjecting it to electrolytic reduc - tion in a molten bath of natural or synthetic cryolite to produce aluminum metal. In 2008, six companies operated fourteen primary aluminum smelters. The smelting required a huge amount of electricity, which hydroelectric dams produced relatively cheaply. The operation of those smelters placed Venezuelafifteenth in production of aluminum, behind Mozambique but ahead of Tajikistan. In the same year, the country ac- counted for 2.9 percent of the world’s bauxite and 1.4 percent of aluminum output. Venezuela consistently ranks in the top twenty-five exporters of aluminum. The main importers of Venezuelan aluminum are the United States, Mexico, Japan, the Netherlands, and Colombia, in descending order. Other Resources Venezuela also is a producer of other mineral com- modities, although none holds more than minor rank- ing in global exports. These minerals are sulfur (6 percent), feldspar (2 percent), and silica sand (1 per- cent). Miscellaneous commodities ranking less than 1 percent include coal, lead, zinc, copper, nickel, gold, titanium, diamonds, and uranium. Most of these com- modities come from mining activities in the Andes Mountains or Guiana Highlands. Richard A. Crooker Further Reading Arnold, Guy. The Resources of the Third World. Chicago: Taylor and Francis, 1997. Crooker, Richard A. Venezuela. Philadelphia: Chelsea House, 2006. Kogel, Jessica Elzea, et al., eds. Industrial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Little- ton, Colo.: U.S. Society for Mining, Metallurgy, and Exploration, 2006. Kozloff, Nikolas. Hugo Chávez: Oil, Politics, and the Challenge to the United States. New York: Palgrave Macmillan, 2006. Salazar-Carrillo, Jorge, and Bernadette West. Oil and Development in Venezuela During the Twentieth Century. Westport, Conn.: Praeger, 2004. Web Sites Central Intelligence Agency The World Fact Book https://www.cia.gov/library/publications/the- world-factbook/index.html Energy Information Administration: Official Energy Statistics from the U.S. Government Venezuela Natural Gas http://www.eia.doe.gov/cabs/Venezuela/ NaturalGas.html International Trade Centre Countries http://www.intracen.org/menus/countries.htm U.S. Geological Survey 2006 Minerals Yearbook, Venezuela http://minerals.usgs.gov/minerals/pubs/country/ 2006/myb3-2006-ve.pdf U.S. Geological Survey Aluminum http://minerals.usgs.gov/minerals/pubs/ commodity/aluminum/mcs-2009-alumi.pdf U.S. Geological Survey Bauxite and Alumina http://minerals.usgs.gov/minerals/pubs/ commodity/bauxite/myb1-2007-bauxi.pdf U.S. Geological Survey Iron http://minerals.usgs.gov/minerals/pubs/ commodity/iron_ore/mcs-2009-feore.pdf See also: Aluminum; Developing countries; Energy politics; Hydroenergy; Iron; Oil and natural gas distri- bution; Organization of Petroleum Exporting Coun- tries; Resources as a source of international conflict. Vermiculite Category: Mineral and other nonliving resources Where Found Vermiculite is found in various parts of the world. Commercial mines for vermiculite are located in Aus- tralia, Brazil, China, Russia, Kenya, Zimbabwe, South Africa, and the United States. Primary Uses Vermiculite has a number of applications in a variety of industries. Some uses for vermiculite include con- struction, agricultural, and horticultural applications. It is also used as fire protection, as insulation, and in various industrial markets. Vermiculite is used as 1296 • Vermiculite Global Resources packaging material for safe shipment of hazardous compounds. Recent uses include nanocomposites for films and coatings. Technical Definition Vermiculite is the geological name given to a large group of hydrated laminar, or layered, minerals that are aluminum-ironmagnesiumsilicatesthatresemble mica in appearance. Vermiculite is a member of the phyllosilicate group of minerals, a group with the characteristic property of expanding into long, worm- like strands with heating. This expansion process is called exfoliation and forms the basis for commercial use of the mineral. Commercial vermiculite typically contains 38 to 46 percent silicon dioxide (SiO 2 ), 16 to 35 percent mag- nesium oxide (MgO), 10 to 16 percent aluminum oxide (A1 2 O 3 ), 8 to 16 percent water, and smaller amounts of several other chemicals. When vermicu- lite is heated and expanded, a color change occurs that depends on the chemicals present and the tem- perature of the furnace. Generally, however, vermicu- lite is gold-brown in color. When vermiculite is heated, it increases ten to thirty times in vol- ume. The bulk density of crude ver- miculite is approximately 640 to 1,120 kilograms per cubic meter. Depend- ing on the size of the granules, the bulk density of expanded vermiculite is about 64 to 160 kilograms per cubic meter. Description, Distribution, and Forms The name vermiculite is derived from a combination of the Latin word ver- miculare, meaning “to breed worms,” and the English suffix “-ite,” which means mineral or rock. The term “ver- miculite” applies to a group of miner- als that have the property of expand- ing into long, wormlike particles when heated. When vermiculite ores exfoli- ate, they expand to many times their original volume. There are two key components of vermiculite’s unique properties. First, vermiculite has a laminar, or layered, crystalline structure with connected layers that expand or unfold linearly, like an accordion. The second key component is trapped water held within vermiculite. When vermic- ulite is heated, this water is rapidly converted into steam, which forces the layers to separate and open, or exfoliate. After exfoliation, the lightweight mate- rial that results is chemically inert, fire-resistant, and odorless. In its expanded form, vermiculite has very low density and thermal conductivity, which makes it useful in many applications. The surface area of exfo- liated vermiculite is large and chemically active, a fea- ture that makes it useful in some chemical processes as an absorbent. Several naturally occurring vermiculite minerals and soils exist, and the identification of specific ones requires scientific analysis. One of the common forms of vermiculite, however, is known as commercial ver- miculite. This is the form that is mined and processed for various industrial and residential uses. Vermiculite ores from mines are derived from rocks that contain large crystals of the minerals biotite and iron-bearing phlogopite. Chemically, vermiculite is a hydrated mag- nesium aluminum silicate. All vermiculite ores contain a range of other min- Global Resources Vermiculite • 1297 Vermiculite is used in construction, agriculture, and horticulture. (USGS) erals that were formed along with the vermiculite in the rock. Although vermiculite ores from some sources have been found to contain asbestos, asbestos is not intrinsic to vermiculite. Only a few vermiculite ores have been found to contain asbestos and gener- ally not more than trace amounts. One vermiculite mine, in Libby, Montana, was found to be contami- nated with substantial amounts of asbestos and was subsequently closed down. Overall, vermiculite is clas- sified a “generally recognized as safe” (GRAS) min- eral, a designation bestowed by the U.S. Food and Drug Administration. History Most accounts indicate that vermiculite and its unique properties were known as early as 1824, when Thomas Webb experimented with the mineral in Worcester, Massachusetts. During his experimentation, he ob- served that heating the mineral resulted in the forma- tion of long, wormlike particles. Because of this prop- erty, he named the mineral vermiculite, or worm breeder, because the heated mineral looked like a mass of worms. Other accounts suggest that vermicu- lite was discovered in 1881 in Libby, Montana, by gold miners, and that in 1919, Edward Alley discovered its unique properties. Vermiculite was thought to be mostly a scientific curiosity until the early 1900’s, when more practical uses for the mineral were discovered. In 1915, the first commercial mining effort of vermiculite was initiated in Colorado, where the mineral was sold as tung ash. There were not enough buyers, however, and the min- ing effort failed. The Zonolite Company started the first successful vermiculite mine in 1923 in Libby, Montana. In 1963, W. R. Grace bought the Zonolite mine, which continued to operate until 1990. While in operation, this mine produced about 80 percent of the world’s vermiculite supply. Vermiculite from the Libby mine was found to be contaminated with a toxic form of naturally occurring asbestos. Obtaining Vermiculite Obtaining vermiculite requires mining. There are many commercial mining operations throughout the world. Locations of some of the predominant com- mercial mines are in Australia, Brazil, China, Kenya, 1298 • Vermiculite Global Resources Data from the U.S. Geological Survey, . U.S. Government Printing Office, 2009.Source: Mineral Commodity Summaries, 2009 110,000 25,000 200,000 100,000 25,000 Metric Tons 210,000180,000150,000120,00090,00060,00030,000 Zimbabwe Russia China Brazil Australia South Africa United States Other countries 15,000 20,000 15,000 Vermiculite: World Mine Production, 2008 South Africa, the United States, and Zimbabwe. As of 2009, the largest vermiculite mining opera- tion in the world was located in the Phalaborwa, or Palabora, region of northeastern Transvaal in South Africa. Other large mining operations are located in the northwesterncorners of China and in the United States, along the eastern Appala- chian range (in Virginia and South Carolina). Some other countries producing significant amounts of vermiculite include Russia, Brazil, and Japan. Vermiculite mines are surface operations in which ore is separated from other minerals. Rocks containing vermiculite are detonated and the loose rocks are fed through crushers and screens to separate the vermiculite from surrounding rocks. Vermiculite flakes are shipped to exfolia- tion plants, where they are heated in a furnace to approximately 540° to 810° Celsius, which causes trapped water to convertrapidly to steam and ver- miculite flakes to expand into wormlike particles. Vermiculite ores may also contain other materi- als, such as mica, quartz, feldspar, and possibly as- bestos. None of the mines in operation poses an asbestos health risk. Uses of Vermiculite Vermiculite has thousands of applications in a variety of industries and has been in use for more than eighty years. Vermiculite is used in construction, agricul- tural, horticultural, and industrial markets. It has ap- plications ranging from use as building insulation to improving potting soil. It is used by pool contractors, by greenhouse growers, in fireproofing, and in many other commercial businesses. Vermiculite has been used extensively as a soil con- ditioner and as an amendment in potting soils. It is used in soil mixes for root cuttings, seed germination, turf grass, plantings, and gardens. Recently, vermicu- lite has been used increasingly in hydroponic garden- ing and for water conservation. Vermiculite improves soil aeration and drainage, while retaining moisture and nutrients necessary for plant growth. Vermiculite is readily mixed with soil, peat, composted bark, and organic compost and creates air channels to allow the soil mix to breathe, while at the same time holding water and nutrients needed by the plant. When used as a carrier for fertilizers, pesticides, or herbicides, or as a bulking agent, vermiculite ensures better distri - bution. Vermiculite has cation exchange properties, which help the growing plant access necessary nutri- ents such as ammonium, potassium, calcium, and magnesium. In the agricultural industry, vermiculite is used in animal feed as a carrierforsupplementsand nutrients. In construction, vermiculite is used in acoustic fin- ishes, in lightweight insulating concrete, in gypsum plaster, and as loft insulation and fire protection. Ver- miculite can be used in combination with many typi- cal binders, such as portland cement, clay, gypsum, and resins. In pools, vermiculite has been used in place of packed sand. Vermiculite has been used as loose-fill insulation in insulated masonry wall systems and as a lightweight aggregate for plaster by mixing with either gypsum or portland cement. Vermiculiteis a major ingredient in most fireproof door cores and safes. Vermiculite is ideal for filling gaps or spaces in existing insulation and was one of the first home in- sulation products used in the United States. When ground into a powder, vermiculite is useful as filler in paints, plastics, and other materials. The absorption properties of vermiculite make it useful as an absorbent packaging material for safe shipment of hazardous liquids. It can hold liquids such as oils, nutrients, chemical mixtures, and special Global Resources Vermiculite • 1299 Light aggregates 35% Horticulture 30% Insulation 5% Other 30% Source: Mineral Commodity Summaries, 2009 Data from the U.S. Geological Survey, . U.S. Government Printing Office, 2009. U.S. End Uses of Vermiculite coatings. It is also used to transport liquids such as fer - tilizers, herbicides, and insecticides, as free-flow sol- ids. Vermiculite is also used to insulate cryogenic tanks. Vermiculite is used in fixation of hazardous material and for nuclear-waste disposal. In the auto- mobile industry, vermiculiteisused in brake pads and shoes. C. J. Stewart Further Reading Kogel, Jessica Elzea, et al., eds. Industrial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Little- ton, Colo.: U.S. Society for Mining, Metallurgy, and Exploration, 2006. Middleton, Gerald V., et al. Encyclopedia of Sediments and Sedimentary Rocks. New York: Springer, 2003. Prothero, Donald R., and Frederic L. Schwab. Sedi- mentary Geology: An Introduction to Sedimentary Rocks and Stratigraphy. 2d ed. New York: Freeman and Company, 2004. Velde, Bruce. Origin and Mineralogy of Clays. New York: Springer, 1995. Web Site The Vermiculite Association http://www.vermiculite.org See also: Agricultural products; Agriculture indus- try; Agronomy; Clays; Fertilizers; Minerals, structure and physical properties of; Sand and gravel; Silicates; Soil. Volcanoes Category: Geological processes and formations Volcanoes or volcanic activity can be a valuable source of natural resources. Some of the economically impor- tant resources derived from volcanic activity are dia- monds, precious metallic minerals, native sulfur, and a nutrient-rich soil produced by the weathering of vol- canic rock. Background All volcanoes are related to the process of plate tec- tonics. Plate tectonics describes the continual move - ment of immense sections (plates) of the Earth’s crust relative to one another. Although this process is in - credibly slow, geologic time is equally long. Both earthquakes and volcanoes most often occur along the boundaries of these plates. They result from the buildup of intense pressure as one plate collides with, or slides past, another. Here old crustalrock is melted as it plunges down into the upper mantle, or new rock forms as magma squeezes out from great fissures in the crust. In the process, old crustal rock is recycled to form new rock that is rich in mineral resources. Major metallic mineral deposits from around the world are associated with plate boundaries past and present. The island of Cyprus is rich in copper that once formed on the seafloor of an ancient oceanic spreading center.The same process has been happen- ing in the Red Sea, where copper-richminerals are be- ing extruded through volcanic activity. The best evidence for submarine deposition of sul- fide minerals by volcanic activity comes from struc- tures called hydrothermal vents, also known as “black smokers.” In appearance, they resemble underwater geysers with cone-type vents emitting black smoke. They result from the seepage of seawater into the hot oceanic basalt crust. This heated seawater then inter- acts with the basalt by extracting iron, copper, sulfur, and other metals from it. Once this mixture erupts onto the seafloor, it mixes with the cold seawater and precipitates sulfide minerals into massive deposits. These become the resources for the future. Volcanoes come in three basic types, based on their particular chemistry. They are named for the volcanic rock produced by each: basalt, andesite, and rhyolite. The most common type of volcano is the basaltic vari- ety. Varieties of basaltic volcanoes can be found along plate boundaries as well as plate centers (such as the one where the Hawaiian Islands formed). The princi- pal rockthatunderliestheworld’s oceans is also basalt. Basaltic Volcanoes Basaltic volcanoes are usually low in silica (approxi- mately 50 percent) and gas content. This type of vol- cano commonly produces fast-moving lava flows and is generally not explosive. The only mineral that is consistently associated with basaltic volcanoes is sul- fur. It forms from sulfur-rich gases that escape from fissures in the cooling lava rock. As the hot gases es- cape, sulfur quickly crystallizes, with its distinctive yel- low color present on the rock. Sulfur is mined at vari- ous volcanic locations. One is Mount Etna on the island of Sicily, where it is an important economic re - source. 1300 • Volcanoes Global Resources Andesitic Volcanoes The second type of volcano results from andesitic magma. It is richer in silica (approximately 60 per- cent) and gas than basaltic volcanoes are. This results in a volcano that can be explosive and can produce a large quantity of lava, depending upon slight varia- tions in its chemical composition. Volcanoes such as this can be extremely dangerous since no one is ever certain what will happen each time they erupt. Mount St. Helens in the state of Washington and Mount Fuji in Japan are two examples of andesitic vol- canoes, which can remain dormant for hundreds of years and then suddenly erupt. The 1980 eruption of Mount St. Helens devastated the area around it. In the aftermath, a rich volcanic ash covered the region. Despite the fact that considerable vegetation was de - stroyed by the eruption and associated flooding, vig- orous plant life returned within a couple of years. This was possible because of the nutrient-rich ash that cre- ated a new soil. Rhyolitic Volcanoes A magma of rhyolitic composition produces the third volcanic type. Compared to the other two, rhyolitic magma is the richest in both its silica (approximately 70 percent) and its gas content. Both gases and fluids present are rich in dissolved metallic minerals. The magma, as it nears the Earth’s surface, first cracks crustal rock and then may erupt with a violent explo- sion. Global Resources Volcanoes • 1301 Beginning of eruption at summit Lava flow and deposition; eruption at lower elevations Subsidence or collapse of summit Cooling; cessation of activity Volcanic Eruption and Caldera Formation Depending ontheirtype and size, volcanoesproducecraters or larger calderas.Ancientcalderas are the sitesof many ore deposits; somemorere - cent calderas are regions of geothermal energy. Often, large hydrothermal mineral deposits are as- sociated with rhyolitic volcanoes. These are deposits of various minerals such as malachite, chalcopyrite, and pyrite, where a metallic element like copper or iron is bonded with sulfur or bonded to a carbonate mole- cule. Such minerals tend to occur in veins where the mineral-rich fluids penetrate fissures in existing rock and then crystallize during cooling. Often gold and/or silver are deposited in this manner. Although such de- posits are common, they do not usually occur in large quantities. Most often, huge amounts of rock must be mined in order to extract relatively small amounts of the valuable metals. The great Bingham copper mine in Utah is an excellent example of such a deposit. Diamond Pipes One important occurrence of a valuable mineral as- sociated with volcanic activity is the diamond pipe. Diamond formationistypically associated with a high- pressure, high-temperature environment. Such con - ditions are present in the Earth’s upper mantle at depths of approximately 200 kilometers. Here dia- monds slowly crystallize within magma. As a result of rapid upward movement, the diamonds are carried along with the magma column. Eventually, upon cool- ing, the magma will form a pipe structure. In shape it somewhat resembles a champagne glass. Most volcanic pipes do not reach the surface and produce a volcano. The more probable situation is that they remain underground as a magma source for an erupting volcano. In those pipes which contain diamonds, the diamonds are disseminated through- out a rock called kimberlite. Erosion may eventually destroy evidence of the volcano, exposing the dia- mond pipe. Erosion also acts as a natural means of ex- tracting the diamonds and then depositing them as sediment in rivers or on beaches. The most important diamond pipes include those of South Africa, Siberia, and western Australia. Paul P. Sipiera 1302 • Volcanoes Global Resources A 1954 photograph detailing the eruption of Kilauea Volcano at Hawaii Volcanoes National Park. (USGS) Further Reading Coleman, Robert G. Geologic Evolution of the Red Sea. New York: Oxford University Press, 1993. Decker, Robert, and Barbara Decker. Volcanoes. 4th ed. New York: W. H. Freeman, 2006. Francis, Peter, and Clive Oppenheimer. Volcanoes.2d ed. New York: Oxford University Press, 2004. Martí, Joan, and Gerald Ernst, eds. Volcanoes and the Environment. New York: Cambridge University Press, 2005. Parfitt, Elisabeth A., and Lionel Wilson. Fundamentals of Physical Volcanology. Malden, Mass.: Blackwell, 2008. Schmincke, Hans-Ulrich. Volcanism. New York: Springer, 2004. Stanton, R. L. Ore Elements in Arc Lavas. New York: Ox- ford University Press, 1994. Tarbuck, Edward J., and Frederick K. Lutgens. Earth: An Introduction to Physical Geology. 9th ed. Illustrated by Dennis Tasa. Upper Saddle River, N.J.: Pearson Prentice Hall, 2008. Wood, Charles A., and Jürgen Kienle, eds. Volcanoes of North America: United States and Canada. New York: Cambridge University Press, 1990. Zeilinga de Boer, Jelle, and Donald Theodore San- ders. Volcanoes in Human History: The Far-Reaching Effects of Major Eruptions. Princeton, N.J.: Princeton University Press, 2005. Web Sites U.S. Geological Survey Volcanoes, by I. Robert Tilling: On-Line Edition http://pubs.usgs.gov/gip/volc U.S. Geological Survey, Volcano Hazards Program About U.S. Volcanoes http://volcanoes.usgs.gov/about See also: Diamond; Earth’s crust; Igneous processes, rocks, and mineral deposits; Magma crystallization; Placer deposits; Plate tectonics; Plutonic rocks and mineral deposits; Seafloor spreading. Global Resources Volcanoes • 1303 W Waste management and sewage disposal Category: Pollution and waste disposal Wastewater consists of domestic and industrial efflu- ent that is collected by a sewage system and conveyed to a central plant, where it is treated prior to release into the ground or, more usually, into a surface water- course. For public health considerations, the properdis- posal of wastewater is a critical parameter in environ- mental planning. Background The Minoan civilization on the island of Crete near Greece had one of the earliest known sewage collec- tion systems in the world (c. 1600 b.c.e.). Ancient Greece had hot and cold water plumbing systems. A large sewer known as the Cloaca Maxima was built during the sixth century b.c.e. in ancient Rome to drain the Forum. The Romans also reused public bathing water to flush public toilets. London had a drainage system by the thirteenth century, but efflu- ent could not be discharged into it until 1815. Sewers were constructed in Paris before the sixteenth cen- tury but fewer than 5 percent of the homes were con- nected to the system by 1893. In general, the wide- spread introduction of sewage collection systems in densely populated areas did not occur until the mid- nineteenth century. For example, the first sewer that was carefully engineered was constructed in Ham- burg, Germany, in 1848. Wastewater disposal systems usually consist of a col- lection system of sewer pipes of varying diameters and materials, a treatment plant of varying size and level of treatment, and an outfall. The outfall may be to the ground or, more commonly, to a receiving water- course such as a stream or (typically along a coast) the ocean. Older wastewater systems are generally com- bined—domestic, industrial, and storm-water runoff are conveyed in the same pipe to the treatment plant. Although cheaper to build initially,combined systems are less desirable, as most of the effluent must bypass the treatment plant during storms,whenstreet runoff increases rapidly. Modern wastewater systems are de - signed to be separate, with different pipes for waste- water and storm runoff. Wherever possible, sewage systems are designed to be below the depth of frost and at a slope that allows gravity drainage. In some low-lying locations and other areas with low relief, the effluent must be pumped, a process that adds expense. Wastewater Characteristics About 60 to 75 percent of the water supplied to a com- munity will wind up as effluent or spent water which must be treated and disposed of. The remaining water is used in industrial processes, lawn sprinkling, and other types of consumptive use. Domestic sewage con- tains varying proportions of human excrement, pa- per, soap, dirt, food waste, and other substances. Much of the waste substance is organic and can be used by organisms of decay (saprophytic microorgan- isms). Accordingly, domestic sewage is biodegrad- able (putrescible) and capable of producing offensive odors. The composition of industrial waste varies from relatively clean rinse water to effluent that can contain corrosive, toxic, flammable, or even explosive materials. This is why communities usually insist on some form of pretreatment by industry before the ef- fluent enters the treatment plant. The organic material in sewage is decomposed by aerobic (oxygen-requiring) bacteria. However, the oxygen that is dissolved in water (DO) can be used up in the process of microbial decomposition. If too much organic waste enters the water body, the bio- chemical oxygen demand (BOD) can exhaust the DO in the water to the extent that the aquatic ecosystem is damaged. Most species of fish die if the DO concen- tration falls below 4 milligrams per liter for periods of time. Some species, such as trout, are even more sensi- tive to DO levels and do best when DO is 8 milligrams per liter or higher. The function of wastewater treatment plants is to produce a discharge that is free of odors, suspended solids, and objectionable bacteria. Coliform bacteria, which are common in the lower intestines of mam - mals, may not be pathogenic themselves but are taken as an indicator of contamination in the watercourse. Treatment processes are often categorized as pri- mary, secondary, or tertiary. The distinction among the three processes is somewhat arbitrary, but the main point is that higher levels of treatment result in a more purified discharge that becomes increasingly more expensive to attain. Primary treatment is mostly mechanical, as it involves the removal of floating and suspended solids by screening and sedimentation in settling basins. As an optional step, chemicals that flocculate or precipitate solids may be added as a means of speeding the process. This type of treatment can remove 40 to 90 percent of the suspended solids and 25 to 85 percent of the BOD. The final effluent may be chlorinated prior to release into a receiving watercourse. Secondary treatment involves biological process- ing after the wastewater has been through primary treatment. One of the two forms of biological process- ing is by means of a trickling filter, in which wastewater is sprayed over crushed stone and allowed to flow in thin films over biologic growths that cover the stone. The organisms in the biologic growths, which include bacteria, fungi, and protozoa, decompose the dis- solved organic materials in the wastewater. Some of the breakdown products in the wastewater, such as carbon dioxide, escape into the atmosphere; others, such as nitrate, which is a mobile ion, remain in solu- tion. Still others are absorbed into the cells of the bio- logic growths. These growths eventually slough off and are carried to settling tanks by the flow of the wastewater. The other type of secondary treatment is known as the activated sludge process. In this proce- dure, flocs of bacteria, fungi, and protozoa are stirred into the wastewater with results that are about the same as trickling filters. Depending upon the effi- ciency of the plant and the nature of the incoming wastewater, both types of biological processes can re- move 50 to 95 percent of the suspended solids and BOD. The efficiency of secondary treatment can be seriously lowered if the design capacity of the plant is overloaded with excessive effluent coming from storm runoff in combined sewers. This is one impor - Global Resources Waste management and sewage disposal • 1305 A worker operates a garbage truck at the Norcal Waste facility in San Francisco. (Getty Images) . Organization of Petroleum Exporting Coun- tries; Resources as a source of international conflict. Vermiculite Category: Mineral and other nonliving resources Where Found Vermiculite is found in various parts. Locations of some of the predominant com- mercial mines are in Australia, Brazil, China, Kenya, 1298 • Vermiculite Global Resources Data from the U.S. Geological Survey, . U.S. Government Printing Office,. explo- sion. Global Resources Volcanoes • 1301 Beginning of eruption at summit Lava flow and deposition; eruption at lower elevations Subsidence or collapse of summit Cooling; cessation of activity Volcanic